Gas turbine engine system with generator

ABSTRACT

In some examples, a system including a gas turbine engine, the engine including a high-pressure (HP) shaft; HP compressor; HP turbine, second shaft; second compressor; second turbine, the second turbine being coupled to the second compressor via the second shaft (e.g., LP shaft); and a generator coupled to the LP shaft. The generator is configured to generate electrical power from rotation of the LP shaft, and increase electrical power generated by the generator to increase a torque applied to the LP shaft by the generator, e.g., in combination with reduction in engine thrust, or in response to the detection of a stall and/or surge of the engine. The increase in torque applied to the second shaft is configured to increase a rate at which a rotational speed of the second shaft decreases, e.g., in combination with the reduction in engine thrust or during the stall/surge of the engine.

TECHNICAL FIELD

The present disclosure relates to gas turbine engine systems that areused, in some examples, for powered vehicles, such as aircraft.

BACKGROUND

A gas turbine engine is a type of internal combustion engine that may beused to power an aircraft, or another moving vehicle. The turbine in agas turbine engine may be coupled to a rotating compressor thatincreases a pressure of fluid flowing into the turbine. A combustor mayadd fuel to the compressed fluid and combust the fuel/fluid combination.The combusted fluid may enter the turbine, where it expands, causing ashaft to rotate. The rotating shaft may drive a propulsor, and thepropulsor may use the energy from the rotating shaft to providepropulsion for the system.

Gas turbine engine powered vehicles, such as aircraft, increasingly useelectrical systems which may operate to provide auxiliary functionsbeyond vehicle propulsion. Electrical systems may be used to replacemechanical, hydraulic, and pneumatic drive systems in gas turbine enginepowered vehicles. Gas turbine engine powered vehicles may includeelectrical energy generating systems to supply power for the electricalsystems.

SUMMARY

The present disclosure is directed to gas turbine engine systemsincluding multiple spools and techniques for operating the same.Examples of the gas turbine engine systems may include a high-pressure(HP) spool and at least one other lower-pressure (LP) spool (e.g., alow-pressure spool and/or an intermediate pressure spool). The gasturbine engine may include a generator coupled to the shaft of the LPspool. The generator may be configured to generate power from therotation of the LP shaft of the LP spool during operation of the turbineengine when the LP shaft is driven by a turbine of the LP spool.

During operation of the turbine engine, the generator may be controlledto apply a tailored level of torque to the LP shaft, e.g., by adjustingthe level of power generated by the generator. For example, incombination with a reduction in thrust and/or deceleration by theturbine engine, the amount of power generated by the generator may beincreased (e.g., by temporarily applying a load or increasing theelectrical load applied on the generator) to increase the torque appliedto the LP shaft by the generator. As another example, in response to adetected stall or surge of the gas turbine engine, the amount of powergenerated by the generator may be increased (e.g., by temporarilyapplying a load or increasing the load applied on the generator) toincrease the torque applied to the LP shaft by the generator. Theadjustments to the torque applied by the generator to the LP shaft mayimprove the operation of the gas turbine engine, e.g., for those reasonsdescribed below.

In some examples, the present disclosure is directed to a gas turbineengine system comprising a gas turbine engine, the gas turbine enginecomprising: a high-pressure (HP) shaft; a HP compressor; a HP turbine,the HP turbine coupled to the HP compressor via the HP shaft; a secondshaft; a second compressor; a second turbine, the second turbine beingcoupled to the second compressor via the second shaft; a generatorcoupled to the second shaft, wherein the generator is configured togenerate electrical power from a rotation of the second shaft, andincrease the electrical power generated by the generator to increase atorque applied to the second shaft by the generator in combination witha reduction in engine thrust.

In some examples, the present disclosure is directed to a method foroperating a system including a gas turbine engine, the gas turbineengine comprising a high-pressure (HP) shaft; a HP compressor; a HPturbine, the HP turbine coupled to the HP compressor via the HP shaft; asecond shaft; a second compressor; a second turbine, the second turbinebeing coupled to the second compressor via the second shaft; and agenerator coupled to the second shaft, the method comprising:generating, using the generator, electrical power from a rotation of thesecond shaft, and increasing the electrical power generated by thegenerator to increase a torque applied to the second shaft by thegenerator in combination with a reduction in engine thrust.

In some examples, the present disclosure is directed to a systemcomprising a gas turbine engine, the gas turbine engine comprising: ahigh-pressure (HP) shaft; a HP compressor; a HP turbine, the HP turbinecoupled to the HP compressor via the HP shaft; a fan; a second shaft; asecond turbine, the second turbine being coupled to the fan via thesecond shaft; and a generator coupled to the second shaft, wherein thegenerator is configured to generate electrical power from a rotation ofthe second shaft, and increase the electrical power generated by thegenerator to increase a torque applied to the second shaft by thegenerator in combination with a reduction in engine thrust.

In some examples, the present disclosure is directed to a systemcomprising a gas turbine engine, the gas turbine engine comprising: ahigh-pressure (HP) shaft; a HP compressor; a HP turbine, the HP turbinecoupled to the HP compressor via the HP shaft; a second shaft; a secondcompressor; a second turbine, the second turbine being coupled to thesecond compressor via the second shaft; a generator coupled to thesecond shaft, wherein the generator is configured to generate electricalpower from a rotation of the second shaft, and wherein the generator isconfigured to, in response to at least one of a stall or a surge of thegas turbine engine, increase the electrical power generated by thegenerator to increase a torque applied to the second shaft by thegenerator during the at least one of the stall or the surge of the gasturbine engine.

In some examples, the present disclosure is directed to a method foroperating a system including a gas turbine engine, the gas turbineengine comprising a high-pressure (HP) shaft; a HP compressor; a HPturbine, the HP turbine coupled to the HP compressor via the HP shaft; asecond shaft; a second compressor; a second turbine, the second turbinebeing coupled to the second compressor via the second shaft; and agenerator coupled to the second shaft, the method comprising:generating, using the generator, electrical power from a rotation of thesecond shaft; detecting at least one of a stall or a surge of the gasturbine engine; and increasing, in response to the detected at least oneof the stall or the surge of the gas turbine engine, the electricalpower generated by the generator to increase a torque applied to thesecond shaft by the generator during the at least one of the stall orthe surge of the gas turbine engine.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram illustrating an example vehicle inaccordance with an example of the present disclosure.

FIGS. 2A-2E are conceptual diagrams illustrating various example gasturbine engine systems including a generator coupled to a lower-pressureshaft of a low pressure or intermediate pressure spool assembly.

FIGS. 3A and 3B are example plots of compressor transient operating lineplots showing corrected air flow versus pressure ratio for alow-pressure compressor or intermediate-pressure compressor of a gasturbine engine during acceleration and deceleration, respectively.

FIG. 4 is a flow diagram illustrating an example technique for operatinga gas turbine engine system in accordance with examples of thedisclosure.

FIG. 5 is a flow diagram illustrating another example technique foroperating a gas turbine engine system in accordance with examples of thedisclosure.

FIG. 6 is a flow diagram illustrating another example technique foroperating a gas turbine engine system in accordance with examples of thedisclosure.

DETAILED DESCRIPTION

The present disclosure is directed to gas turbine engine systems, e.g.,for gas turbine engine powered vehicles such an aircraft, and techniquesfor operating the same. For ease of description, examples of thedisclosure will be primarily described in the context of aircraft as agas turbine engine powered vehicle. However, examples of the disclosureare not limited to aircraft.

Gas turbine engine powered aircraft increasingly require significantamount of additional power beyond that generated by the one or more gasturbine engines used by the aircraft for main propulsion. In someexamples, electrical systems may be used to replace mechanical,hydraulic, and pneumatic drive systems in gas turbine engine poweredvehicles, while also providing one or more auxiliary functions to theaircraft not directly related to propulsion. Those electrical systemsmay increase the electrical load requirements for the vehicle.

Electric machines that function as electric generators may be employedby gas turbine combustion engine power aircraft to satisfy the transientand/or continuous electrical loads associated with the electricalsystem(s). For example, a gas turbine engine having a low-pressure spoolassembly (e.g., including a low-pressure compressor and/or fan and alow-pressure turbine connected by a low-pressure shaft) andhigh-pressure spool assembly (e.g., including a HP pressure compressorand a HP turbine connected by a HP shaft) may include an electricgenerator that generates electricity from the rotation of thelow-pressure spool shaft. The electrical power extracted from thelow-pressure spool shaft may be used to supply power to various aircraftsystems (e.g., electrical systems of the vehicle system that requireelectrical energy to operate, such as aircraft anti-ice heating, weaponsystems, navigation systems including radar, environmental coolingsystems (ECS)).

The present disclosure is directed to gas turbine engine systemsincluding multiple spool assemblies and techniques for operating thesame. Examples of the gas turbine engine systems may include ahigh-pressure (HP) spool assembly and at least one other lower pressure(LP) spool assembly (e.g., a low-pressure spool assembly and/or anintermediate pressure spool assembly). The gas turbine engine mayinclude a generator coupled to the LP shaft of the LP spool assembly sothat the generator generates power from the rotation of the LP shaft.

When the generator generates power from the rotation of the LP shaft,the generator applies an amount of torque on the LP shaft, e.g., atorque that acts to resist the rotation of the LP shaft. As describedherein, the amount of torque applied by the generator may be modulatedor otherwise adjusted during the operation of the gas turbine engine,e.g., when the gas turbine engine is providing propulsion for anaircraft. For example, the amount of torque applied by the generator tothe LP shaft (e.g., in opposition to the rotation of the LP shaft) maybe adjusted by adjusting the level of power generated by the generator.When the amount of power generated by the generator is increased, theamount of torque applied to the LP shaft may also increase. Similarly,when the amount of power generated by the generator is decreased, theamount of torque applied to the LP shaft may also decrease.

Examples of the present disclosure may adjust (e.g., dynamically) theamount of torque applied by the generator on the LP shaft during theoperation of a gas turbine engine to provide for improved operation ofthe gas turbine engine. For example, in some instances, the amount oftorque applied to the LP shaft by the generator may be increased incombination with a reduction in thrust by a gas turbine engine (e.g.,for deceleration of the aircraft) by increasing the power generated bythe generator from the LP shaft rotation for a period of time. Theincrease in power generated by the generator may be accomplished byincreasing an electrical load for the generator, e.g., by an energystorage device to charge a battery and/or by electrical systems of theaircraft that may otherwise be supplied with power from another powersource other than the generator.

As will be described below, in some examples the increase in torqueapplied by the generator to the LP shaft may decrease the deviation froma working line compared to the deviation that may normally result duringthe initial deceleration of an aircraft without such an increase intorque applied to the LP shaft. In some examples, the increase in torqueapplied by the generator to the LP shaft may increases the rate at whicha rotational speed of the LP shaft decreases during the reduction in theengine thrust. In some examples, the increase in torque applied to theLP shaft is configured to reduce a time period over which the rotationalspeed of the LP shaft decreases during the reduction in engine thrust.In some examples, the increase in torque applied to the LP shaft isconfigured to decrease the transient deviation of the LP compressor fromthe working line of the LP compressor during the reduction in enginethrust. In each instance, the increase in torque applied to the LP shaftmay be configured to prevent stall or surge of the LP compressor due tothe HP compressor decelerating faster than the LP compressor.

Additionally, or alternatively, in some examples, the amount of torqueapplied to the LP shaft by the generator may be increased in combinationwith a stall or surge of a gas turbine engine by increasing the powergenerated by the generator from the LP shaft rotation for a period oftime. As described below, the increased amount of torque during thestall or surge may cause the LP rotor(s) (e.g., low-pressure compressor,fan, and/or intermediate-pressure compressor) to reduce speed while theHP spool remains at a relatively high-speed demanding higher flow. Thismay cause a reduction, e.g., in the low-pressure compressor, fan, and/orIP compressor working line and allow the engine to recover from a stallor surge.

As noted above, some examples of the present disclosure relate to gasturbine engine that include an HP spool assembly and one or morelower-pressure spool assemblies (e.g., such as a low-pressure spoolassembly or intermediate spool assembly). For ease of illustration,examples of the disclosure are described primarily with regard to dualspool gas turbine engines including a HP spool assembly, a low-pressurespool assembly (e.g., including a low-pressure fan and/or a low-pressurecompressor), and a generator that generates power from rotation of thelow-pressure shaft. However, the techniques described herein may also beapplied to intermediate-pressure spool assemblies with such a generatorin addition to, or as an alternative to, the low-pressure spoolassemblies.

With reference to FIGS. 3A and 3B, the working line characteristic of anLP compressor for an example dual spool assembly gas turbine engine isshown in FIG. 3A for the acceleration of such a gas turbine engine.Initially, the LP compressor shows a small increase in its working lineto satisfy the reduced mass flow into the HP compressor, but as soon asthe HP spool begins to speed up the LP spool lags behind and so it dragsthe working line down, increasing the stall/surge margin. During adeceleration the opposite characteristic holds, characterized by aninitial decrease in stall/surge margin as shown in FIG. 3B. The plots ofFIGS. 3A and 3B may also be representative of an intermediate-pressurecompressor. In FIGS. 3A and 3B, the pressure ratio on the vertical axisis the pressure ratio across the LP compressor (or intermediate pressurecompressor or fan). The horizontal axis represents a compressor flowfunction which is proportional to compressor corrected flow. W iscompressor physical flow. T is compressor inlet temperature and P iscompressor inlet pressure. For corrected flow: W*SQRT(Theta)/Delta;Theta=T/standard temperature; and Delta=P/standard pressure

When the LP compressor (e.g., low-pressure compressor and/orintermediate-pressure compressor) enters into a stall or surge, thestresses on the blades can increase substantially and additionallysignificant thrust can be lost. Therefore, during design of an engine,all the factors that influence stall margin must be accounted for suchthat positive margin is maintained throughout the life of the gasturbine engine. The accounting of items includes things such asincreases in tip clearance due to rub-in (which will lower the stallline), manufacturing variability (which can affect both the stall andworking line), as well as engine transients as just discussed. If it ispossible to reduce the amount of stall margin that must be maintained indesign, for example through improved manufacturing tolerances (or, e.g.,example techniques described herein), then the LP compressor may bedesigned such that equivalent thrust can be provided with a smallerdiameter compressor, which in turn will make a smaller diameter nacellereducing the overall airframe weight and drag. Additionally, examples ofthe present disclosure are described in some examples with fullauthority digital engine control (FADEC) logic being employed to controlthe operation of the gas turbine engine system. However, the use of anysuitable control systems is contemplated.

Examples of the present disclosure relate to techniques, and gas turbineengine systems for performing such techniques, that include increasingthe amount of power generation on a generator (and therefore torque)connected to a LP spool shaft during the initial deceleration of theengine. In some instances, the additional torque may start to be appliedthrough the FADEC logic even before the thrust is reduced (e.g., beforethe fuel flow is reduced to the combustor). By adding this torque to theLP spool, the engine may be able to decelerate faster than wouldotherwise be possible allowing reduced working line excursion and inturn improved stall margin. This improved stall margin characteristiccan be leveraged in the engine design to reduce weight and airframe dragas mentioned previously. It is proposed that, in some examples, theenergy generated by the generator be stored in an appropriate energystorage means, for example a battery, and/or directed to otherelectrical systems of an aircraft such as an environmental controlsystem (ECS) of an aircraft (e.g., where an increased electrical load istemporarily applied with the ECS).

One potential challenge with this approach is that a gas turbine enginemay have reduced, and perhaps insufficient stall margin should thegenerator fail. Accordingly, an engine design is also proposed that inthis scenario the FADEC reverts to a reversionary logic that limits theacceleration and deceleration rates of the gas turbine engine such thatstall margin can be maintained. Alternatively, or additionally, foremergency scenarios, such as during an aborted takeoff, it may beacceptable to allow the reduced stall margin since a nominal engine mayhave more margin than a deteriorated ‘worst engine’ that must bedesigned for. The impacts of having a stall/surge during and event suchas an aborted takeoff may also be acceptable as the engine cansubsequently be inspected for any damage. An example decision flow logicfor this implementation is described further below with regard to FIG. 6.

Gas turbine engines may also incorporate stall/surge recovery logic thatis executed by the FADEC when a stall or surge is detected. In someexamples of the present disclosure, techniques that include the increasethe LP generator torque/power generation in response to a surge or stalldetection may be employed, e.g., by incorporating the action into the LPstall or surge recovery logic as well. In such instances, the addedtorque may cause the LP rotor to reduce speed while the HP spool remainsat a relatively high-speed demanding higher flow. This may cause areduction in the fan working line and allow the fan to recover from astall or surge. In some examples, such stall/surge recovery logic isonly executed in the case of a stall/surge and not necessarily during acommanded thrust change, as in the case described above.

FIG. 1 is a conceptual diagram illustrating an example vehicle inaccordance with an example of the present disclosure. In the example ofFIG. 1 , the vehicle includes an aircraft 10. In other examples, thevehicle may include any type of gas turbine engine-powered vehicle,including one or more types of air vehicles; land vehicles, includingbut not limited to, tracked and/or wheeled vehicles; marine vehicles,including but not limited to surface vessels, submarines, and/orsemi-submersibles; amphibious vehicles; or any combination of one ormore types of air, land, and marine vehicles. The vehicle may be manned,semiautonomous, or autonomous.

Aircraft 10 includes a fuselage 12, wings 14, an empennage 16, two gasturbine engine systems 18A and 18B (collectively, “gas turbine engines18”) as main propulsion engines. In other examples, aircraft 10 mayinclude a single gas turbine engine 18 or a plurality of propulsionsystems 18. As illustrated in FIG. 1 , aircraft 10 is a twin-engineturbofan aircraft. In some examples, aircraft 10 may be any fixed-wingaircraft, including turbofan aircraft, turbojet aircraft, and turbopropaircraft. In some examples, aircraft 10 may be a rotary-wing aircraft ora combination rotary-wing/fixed-wing aircraft. Aircraft 10 may employany number of wings 14. Empennage 16 may employ a single or multipleflight control surfaces. Gas turbine engines 18 may be the mainpropulsion systems of aircraft 10. Aircraft may also have more than twoengines such as three or four engines or may have a single engine.

In accordance with some examples of the disclosure, one or both of gasturbine engine systems 18A and 18B may include a HP spool, one or morelower pressure (LP) spools (e.g., a single low-pressure spool or alow-pressure spool and intermediate pressure (IP) spool), and agenerator coupled to a rotating shaft of a lower pressure (LP) spool.The systems may be configured such that the generator generates powerfrom the rotation of the LP shaft, which results in a torque applied tothe LP shaft. The amount of torque applied to the LP shaft may beselectively modified or otherwise adjusted based on the operation of thegas turbine engine (such as changes in thrust) to adjust the amount oftorque applied to the LP shaft, e.g., to generally improve the operationof the gas turbine engine as described herein.

FIG. 2A is a conceptual and schematic diagram illustrating gas turbineengine system 18A in accordance with an example of the presentdisclosure. Although described herein as with respect to an aircraftpropulsion system, in other examples, gas turbine engine 18A may be apropulsion system for providing propulsive thrust to any type of gasturbine engine powered vehicle, as discussed above, or configured toprovide power any suitable nonvehicle system including gas turbineengine 18A. Engine 18B may be the same or similar to engine 18A in FIG.1 .

Engine 18A may be a primary propulsion engine that provides thrust forflight operations of aircraft 10. In the example of FIG. 2A, engine 18Ais a two-spool engine having a high-pressure (HP) spool (rotor) 24 and alow-pressure spool (rotor) 26. In other embodiments, engine 20 mayinclude three or more spools, e.g., may include an IP spool and/or otherspools and/or partial spools, e.g., on-axis or off-axis compressorand/or turbine stages (i.e., stages that rotate about an axis that isthe same or different than that of the primary spool(s)). In one form,engine 18A is a turbofan engine. In other embodiments, engine 18A may beany other type of gas turbine engine, such as a turboprop engine, aturboshaft engine, a propfan engine, a turbojet engine or a hybrid orcombined cycle engine. As a turbofan engine, low-pressure spool 26 isoperative to drive a propulsor 28 in the form of a fan, which may bereferred to as a fan system. As a turboprop engine, low-pressure spool26 powers a propulsor 28 in the form of a propeller system (not shown),e.g., via a reduction gearbox (not shown). In other embodiments,propulsor 28 may take other forms, such as one or more helicopter rotorsor tilt-wing aircraft rotors, for example, powered by one or moreengines 18A in the form of one or more turboshaft engines.

In one form, engine 18A includes, in addition to fan 28, a bypass duct30, a high-pressure (HP) compressor 32, a diffuser 34, a combustor 36, ahigh-pressure (HP) turbine 38, a low-pressure turbine 40, a nozzle 42A,a nozzle 42B, and a tailcone 46, which are generally disposed aboutand/or rotate about an engine centerline 49. In other embodiments, theremay be, for example, an intermediate pressure spool having anintermediate pressure turbine or other turbomachinery components, suchas those mentioned above. In one form, engine centerline 49 is the axisof rotation of fan 28, HP compressor 32, HP turbine 38 and turbine 40.In other embodiments, one or more of fan 28, HP compressor 32, HPturbine 38 and turbine 40 may rotate about a different axis of rotation.

In the depicted example, engine 18A core flow is discharged throughnozzle 42A, and the bypass flow from fan 28 is discharged through nozzle42B. In other embodiments, other nozzle arrangements may be employed,e.g., a common nozzle for core and bypass flow; a nozzle for core flow,but no nozzle for bypass flow; or another nozzle arrangement. Bypassduct 30 and HP compressor 32 are in fluid communication with fan 28.Nozzle 42B is in fluid communication with bypass duct 30. Diffuser 34 isin fluid communication with HP compressor 32. Combustor 36 is fluidlydisposed between HP compressor 32 and HP turbine 38. Turbine 40 isfluidly disposed between HP turbine 38 and nozzle 42A. In one form,combustor 36 includes a combustion liner (not shown) that contains acontinuous combustion process. In other embodiments, combustor 36 maytake other forms, and may be, for example, a wave rotor combustionsystem, a rotary valve combustion system, a pulse detonation combustionsystem, a continuous detonation combustion system and/or a slingercombustion system, and may employ deflagration and/or detonationcombustion processes.

Fan system 28 includes a fan rotor system 48 driven by low-pressurespool 26. In various examples, fan rotor system 48 may include one ormore rotors that are powered by turbine 40. In various embodiments, fan28 may include one or more fan vane stages (not shown in FIG. 2A) thatcooperate with fan blades (not shown) of fan rotor system 48 to compressair and to generate a thrust-producing flow. Bypass duct 30 is operativeto transmit a bypass flow generated by fan 28 around the core of engine18A. HP compressor 32 includes a compressor rotor system 50. In variousexamples, compressor rotor system 50 includes one or more rotors (notshown) that are powered by HP turbine 38. HP compressor 32 also includesa plurality of compressor vane stages (not shown in FIG. 2A) thatcooperate with compressor blades (not shown) of compressor rotor system50 to compress air. In various embodiments, the compressor vane stagesmay include a compressor discharge vane stage and/or one or morediffuser vane stages. In one form, the compressor vane stages arestationary. In other embodiments, one or more vane stages may bereplaced with one or more counter-rotating blade stages.

HP turbine 38 includes a turbine rotor system 52. In variousembodiments, turbine rotor system 52 includes one or more rotors havingturbine blades (not shown) operative to extract power from the hot gasesflowing through HP turbine 38 (not shown), to drive compressor rotorsystem 50. HP turbine 38 also includes a plurality of turbine vanestages (not shown) that cooperate with the turbine blades of turbinerotor system 52 to extract power from the hot gases discharged bycombustor 36. In one form, the turbine vane stages are stationary. Inother embodiments, one or more vane stages may be replaced with one ormore counter-rotating blade stages. Turbine rotor system 52 is drivinglycoupled to compressor rotor system 50 via a shafting system 54 (alsoreferred to as high-pressure (HP) shaft 54). Turbine 40 includes aturbine rotor system 56. In various embodiments, turbine rotor system 56includes one or more rotors having turbine blades (not shown) operativeto drive fan rotor system 48. Turbine 40 may also include a plurality ofturbine vane stages (not shown in FIG. 2A) that cooperate with theturbine blades of turbine rotor system 56 to extract power from the hotgases discharged by HP turbine 38. In one form, the turbine vane stagesare stationary. In other embodiments, one or more vane stages may bereplaced with one or more counter-rotating blade stages. Turbine rotorsystem 56 is drivingly coupled to fan rotor system 48 via shaftingsystem 58 (also referred to as low-pressure shaft 58). In variousembodiments, shafting systems 54 and 58 include a plurality of shaftsthat may rotate at the same or different speeds and directions fordriving fan rotor system 48 rotor(s) and compressor rotor system 50rotor(s). For ease of description, shafting system 54 of HP spool 24 isdescribed primarily as HP shaft 54 but is it recognized that system 54is not limited to a single shaft. Likewise, shafting system 58 oflow-pressure spool 26 is described primarily as low-pressure shaft 58but is it recognized that system 58 is not limited to a single shaft.Turbine 40 is operative to discharge the engine 20 core flow to nozzle42A.

During normal operation of gas turbine engine 18A, air is drawn into theinlet of fan 28 and pressurized. Some of the air pressurized by fan 28is directed into HP compressor 32 as core flow, and some of thepressurized air is directed into bypass duct 30 as bypass flow. HPcompressor 32 further pressurizes the portion of the air receivedtherein from fan 28, which is then discharged into diffuser 34. Diffuser34 reduces the velocity of the pressurized air, and directs the diffusedcore airflow into combustor 36. Fuel is mixed with the pressurized airin combustor 36, which is then combusted. The hot gases exitingcombustor 36 are directed into turbines 38 and 40, which extract energyin the form of mechanical shaft power to drive HP compressor 32 and fan28 via respective HP shaft 54 and low-pressure shaft 58. The hot gasesexiting turbine 40 are discharged through nozzle system 42A, and providea component of the thrust output by engine 20.

As shown in FIG. 2A, engine 18A includes generator 60. In theillustrated example, generator 60 is positioned between fan system 48and HP compressor 32 along centerline 49. Generator 60 may include anysuitable type and/or arrangement of an electrical machine such as anelectro-mechanical generator that operates in the manner describedherein, e.g., by generating power from the rotation of low-pressureshaft 58, with the amount of power being generated being adjusted insome circumstances based on the operation of engine 18A. For example,the amount of power being generated by generator 60 may be increased incombination with a decrease in thrust by engine 18A, e.g., totemporarily increase the torque applied on low-pressure shaft 58 whenthe thrust generated by engine 18A is initially reduced.

In some examples, generator 60 may be positioned in front of the nosecone or spinner of engine 18A. In other examples, rather than beingembedded and positioned coaxially with low-pressure shaft 58, generator60 may be mounted on an externally mounted gearbox which is power by ashaft driven from the LP rotor (or IP rotor in a three-spool engine).

In some examples, generator 60 may be an electrical machine that isconfigured to be selectively operated as an electric generator or anelectric motor. Example of suitable motor-generators 60 may include oneor more of the examples of the motor-generator and motor generatorassemblies disclosed within U.S. patent application Ser. Nos.15/590,623; 15/590,606; 15/590,581; and Ser. No. 15/590,554, filed May9, 2017 and the example electrical machines describes in U.S. patentapplication Ser. No. 15/135,167 filed Dec. 19, 2013. The entire contentof these applications are incorporated by reference herein. In someexamples, generator 60 may be selectively operated to extract and/orprovide power to the low-pressure shaft 58. For example, generator 60may be configured for selective operation between a generation mode togenerate electrical power from rotation of the low-pressure turbine 40and in a drive or motor mode to receive electrical power for applyingrotational force to the low-pressure shaft 58. However, in some examplesof the disclosure, generator 60 is an electrical machine that operatesin a generator mode but not a motor mode.

In the example of FIG. 2A as well as the other examples turbine enginesystems described herein, generator 60 may be an embedded electricalmachine in that the stator and rotor of electrical machine core arepositioned coaxially with low-pressure shaft 58. The stator of generator60 may be fixed against rotation relative to the low-pressure shaft 58and a rotor may be coupled to the low-pressure shaft 58 for rotationtherewith. The rotor may be attached to a mount of the low-pressureshaft 58 positioned axially between shaft bearings of the low-pressureshaft 58. The stator may include a number of stator windings positionedradially outward of the rotor, such that each stator winding is arrangedin electromagnetic communication with the rotor 44. In other examples,generator 60 may include a stator and rotor positioned non-coaxially,e.g., where the rotor of generator 60 is rotationally coupled tolow-pressure shaft 32 via one or more other shafts and suitable gearing.

FIG. 2B is a schematic functional diagram illustrating additionalcomponents of engine system 18A of FIGS. 1 and 2A, and like features aresimilarly numbered. As noted above, engine system 18A may be a gasturbofan system. Engine 18A may include fan rotor system 28 that isrotationally coupled to low-pressure turbine 40 by low-pressure shaft58, and HP compressor 32 rotationally coupled to HP turbine 38 by HPshaft 54. The speed of shaft 54 driving the HP compressor 32 may bedifferent from that of the speed of shaft 58 driving the fan rotorsystem 28. The combination of HP compressor 32, HP turbine 38 and HPshaft 54 may be referred to as the HP spool assembly 24 or HP spool 24.

Unlike that of engine 18A shown in FIG. 2A, engine 18A of FIG. 2Bincludes low-pressure compressor 29. Low-pressure compressor 29 iscoupled to rotationally coupled to low-pressure turbine 40 bylow-pressure shaft 58. In some examples, low-pressure compressor 29 maybe referred to as a booster. In some examples, low-pressure compressor29 may be similar to that of HP compressor 32 and may include acompressor rotor system (not shown in detail in FIG. 2B). In variousexamples, the compressor rotor system includes one or more rotors (notshown) that are powered by low-pressure turbine 40. Low-pressurecompressor 29 may also include a plurality of compressor vane stages(not shown in FIG. 2B) that cooperate with compressor blades (not shown)of the compressor rotor system to compress air. In various embodiments,the compressor vane stages may include a compressor discharge vane stageand/or one or more diffuser vane stages. In one form, the compressorvane stages are stationary. In other embodiments, one or more vanestages may be replaced with one or more counter-rotating blade stages.In operation, low-pressure compressor 29 may operate to increase thepressure of the intake air, which is then further increase in pressureby HP compressor 32.

The combination of fan system 28, low-pressure compressor 29,low-pressure turbine 40 and low-pressure shaft 58 may be referred to asthe low-pressure spool assembly 26 or low-pressure spool 26. Similar tothat of engine 18A in FIG. 2A, engine 18A of FIG. 2B includes generator60, which is operably coupled to low-pressure shaft 58, e.g., in anembedded (co-axial) with low-pressure shaft 58 or non-co-axial.

Engine system 18A also includes rectifier/inverter 62. The electricalsystems 65 and power storage device 66 may be part of the aircraftsystem 10. System 10 also includes controller 64. Controller 64 mayinclude control circuitry for the control of the engine systems and maycontrol the rectifier 62. Controller 64 may include one or a combinationof controllers as part of a control system that controls the operationof engine 18A and/or other components of system 10. For example,controller 64 represents more than one controller, wherein the more thanone controller includes an engine controller. The engine controller maybe part of the engine but may be physically located on the aircraft. Oneof the individual controllers of controller 64 controls the electricalloads and battery in aircraft 10 as part of system 10, e.g., in themanner described herein for increase the torque applied by generator 60on shaft 58. As illustrated, all or a portion of controller 64 may belocated on aircraft 10; however there may be some configuration where anengine controller is mounted on engine 18A.

For generator 60 the power is used by the electrical system 65 and powerstorage system 66, which are devices that can absorb relatively largeamounts of power. As described herein, the amount of electrical loadapplied by electrical system 65 and/or power storage system 66 ongenerator 60 may be varied to vary the amount of torque load applied bygenerator 60 on low-pressure shaft 58, e.g., to decrease the rotationalspeed of low-pressure shaft 58 over a shorter period of time incombination with the reduction in thrust by engine 18A. The generatoroutput voltage may be controlled by the rectifier 62 that may controlthe power input to power storage 66 on a DC bus. If the rectifier 62 ispowering a DC bus with multiple power sources (not shown) then it mayalso control the generator power to the electrical system 65.

Controller 64 may be configured to control the components of engine 18Aand/or aircraft 10 individually and selectively such that engine 18A andsystem 10 more generally implement the techniques described herein.Controller 64 may comprise any suitable arrangement of hardware,software, firmware, or any combination thereof, to perform thetechniques attributed to controller 64 herein. Examples of controller 64include any of one or more microprocessors, digital signal processors(DSPs), application specific integrated circuits (ASICs), fieldprogrammable gate arrays (FPGAs), processing circuitry, or any otherequivalent integrated or discrete logic circuitry, as well as anycombinations of such components. When controller 64 includes software orfirmware, controller 64 further includes any necessary hardware forstoring and executing the software or firmware, such as one or moreprocessors or processing units. In some examples, all or portions ofcontroller 64 may be embodied in a full authority digital engine control(FADEC) including an electronic engine controller (EEC) or enginecontrol unit (ECU) and related accessories that control one or moreaspects of the operation of engine system 18A.

In general, a processing unit may include one or more microprocessors,DSPs, ASICs, FPGAs, or any other equivalent integrated or discrete logiccircuitry, as well as any combinations of such components. Although notshown in FIG. 2B, controller 64 may include a memory configured to storedata. The memory may include any volatile or non-volatile media, such asa random access memory (RAM), read only memory (ROM), non-volatile RAM(NVRAM), electrically erasable programmable ROM (EEPROM), flash memory,and the like. In some examples, the memory may be external to controller64 (e.g., may be external to a package in which controller 64 ishoused).

Although controller 64 is generally described as being the primary unitfor controlling each of the engine components of system 18A forperforming the techniques described herein, in some examples, theindividual components of system 18A may include additional functionalityfor performing some or all the operations described below with respectto controller 64. For example, a combination of one or more of HPcompressor 32, turbines 38, 40, fan system 28, low-pressure compressor29, generator 60, rectifier/inverter 62, and the like may includecomponents for controlling the operation of system 18A in the mannerdescribed herein. As described herein, generator 60, is configured togenerate power from the rotation of shaft 58, e.g., as driven by turbine40. The electrical energy generated by generator 60 in a generator modemay be used to provide operational power to one or more electricallyoperated systems 65 of vehicle 10 (FIG. 1 ). In some examples, generator60 may be configured to generate continuous aircraft or transient systempower also defined by the desired end user application. Exampleelectrical systems 65 that may be powered by generator 60 includehydraulic and/or pneumatic drive systems, environmental control systems,communications systems, directed energy systems, radar systems andcomponent cooling systems. Electrical systems 65 may be any systemhaving electrical components requiring power to operate. When operationpower is supplied by a generator such as generator 60, electrical system65 may apply an electrical load on the generator in order for electricalsystem 65 to operate in the desired manner.

Additionally, or alternatively, all or some of the power generated bygenerator 60 may be stored by power storage device 66. In such anexample, rectifier/inverter 62, under the control of controller 64 mayincrease its output voltage to input all or a portion of the powergenerated by generator 60 as direct current to power storage device 66for storage of the power. Power storage device 66 may be any suitabledevice such as one or more suitable batteries or capacitors. Engine 18Amay utilize the power stored in power storage device at times when thepower generated by generator 60 is relatively low. Power storage device66 may apply (e.g., selectively) an electrical load on generator 60 torecharge the power storage device (e.g., battery). The electrical loadapplied by power storage device 66 on generator 60 may increase thetorque on LP shaft 58.

As described herein, the amount of power generated by generator 60 maybe adjusted based during the operation of engine 18A, e.g., when engine18 a is providing propulsion for aircraft 10. The amount of powergenerated by generator 60 may be adjusted by adjusting the electricalload applied to generator 60, e.g., by power storage 66 and/orelectrical systems 65. For example, an increase in electrical loadapplied by power storage 66 and/or electrical systems 65 on generator 60may increase the power generated/output by generator 60. Conversely, adecrease in electrical load applied by power storage 66 and/orelectrical systems 65 on generator 60 may decrease the powergenerated/output by generator 60. An adjustment to the amount of powergenerated by generator 60 may result in a corresponding adjustment tothe amount of torque applied to low-pressure shaft 58, where the torqueapplied to the low-pressure shaft 58 may be resistive to the rotation ofshaft 58. For example, an increase in electrical load applied by powerstorage 66 and/or electrical systems 65 on generator 60 may increase thetorque applied by generator 60 on LP shaft 58. Conversely, a decrease inelectrical load applied by power storage 66 and/or electrical systems 65on generator 60 may decrease the torque applied by generator 60 on LPshaft 58. In this manner, generator 60 may be controlled by theelectrical loads to apply a tailored amount of torque to low-pressureshaft 58 at a given point in time by selectively adjusting the amount ofpower generated by generator 60, e.g., in combination with theacceleration and/or deceleration of engine 18A.

As noted above, in some examples, the electrical load applied byelectrical system 65 and/or power storage system 66 on generator 60 maybe increased to increase the torque applied by generator 60 tolow-pressure shaft 58 in combination with the deceleration of aircraft10 (or other reduction in thrust generated by engine 18A). The increasein torque may decrease the deviation from a working line compared to thedeviation that may normally result during the initial deceleration ofaircraft 10 without such an increase in torque applied to low-pressureshaft 58.

FIG. 2C is a schematic functional diagram illustrating another exampleof engine 18A in FIG. 1 . Engine 18A in the example of FIG. 2C may besubstantially similar to that of the example of FIG. 2B, and likefeatures are similarly numbered. However, in the example of FIG. 2C,engine 18A may be a gas turbojet system compared to a gas turbofansystem such as that shown in FIGS. 2A and 2B. LP shaft 58 in the exampleof FIG. 2C drives fan 28 but there is no bypass like that in FIGS. 2Aand 2B so substantially all the intake air passes through the core e.g,all the fan air being absorbed by HP compressor 32. In some examples,engine 18A in FIG. 2C may include a low-pressure compressor (not shown)driven by LP shaft 58 along with fan 28, e.g., in a manner similar tothat shown in the example of FIG. 2B with low-pressure compressor 29. Insuch an example, the lower pressure spool assembly may include thelow-pressure compressor 29, fan 28, LP shaft 58 and LP turbine 40.

As described herein, generator 60, under the control of rectifier 62, isconfigured to generate power from the rotation of shaft 58, e.g., asdriven by turbine 40. When generator 60 is generating power from therotation of shaft 58, a torque may be applied on shaft 58 of the LPspool, e.g., in opposition to the rotation of shaft 58. In accordancewith examples of the disclosure, the amount of torque applied bygenerator 60 to shaft 58 of the LP spool may be tailored or otherwiseselectively adjusted by selectively adjusting the amount of powergenerated by generator 60.

FIG. 2D is a schematic functional diagram illustrating another exampleof engine 18A in FIG. 1 . Engine 18A in the example of FIG. 2D may besubstantially similar to that of the example of FIG. 2B, and likefeatures are similarly numbered. However, in the example of FIG. 2D,engine 18A may be a three-spool, gas turbofan system compared to atwo-spool system such as that shown in FIGS. 2A and 2B. For example, inFIG. 2D, engine 18A includes IP compressor 31 and IP turbine 41, whichare rotationally coupled by IP shaft 55 with turbine 41 drivingcompressor 31 by shaft 55. In such an example, engine 18A may include anintermediate pressure spool assembly including IP compressor 31, IPshaft 55 and IP turbine 41, along with fan 28, turbine 40, and shaft 58,and the HP spool assembly including HP compressor 32, HP turbine 38, andHP shaft 54.

IP compressor 31 may be similar to that of HP compressor 32 and mayinclude a compressor rotor system (not shown in detail in FIG. 2D). Invarious examples, the compressor rotor system includes one or morerotors (not shown) that are powered by IP turbine 40. IP compressor 31may also include a plurality of compressor vane stages (not shown inFIG. 2D) that cooperate with compressor blades (not shown) of thecompressor rotor system to compress air. In various embodiments, thecompressor vane stages may include a compressor discharge vane stageand/or one or more diffuser vane stages. In one form, the compressorvane stages are stationary. In other embodiments, one or more vanestages may be replaced with one or more counter-rotating blade stages.In operation, IP compressor 31 may operate to increase the pressure ofthe air from fan 28, which is then further increased in pressure by HPcompressor 32.

IP turbine 41 may be similar to that of HP turbine 38 or turbine 40. Invarious embodiments, turbine 41 includes a rotor system (not shown) thatincludes one or more rotors having turbine blades (not shown) operativeto extract power from the hot gases flowing through IP turbine 41 todrive IP compressor 31 via IP shaft 55. Engine 18A of FIG. 2D alsoincludes generator 60, which is operably coupled to IP shaft 55, e.g.,in an embedded (co-axial) with IP shaft 55 or non-co-axial. Generator60, under the control of controller 64, is configured to generate powerfrom the rotation of shaft 55, e.g., as driven by IP turbine 41. Whengenerator 60 is generating power from the rotation of shaft 55, a torquemay be applied on shaft 55 of the IP spool, e.g., in opposition to therotation of shaft 55. In accordance with examples of the disclosure, theamount of torque applied by generator 60 to shaft 55 of the IP spool maybe tailored or otherwise selectively adjusted by selectively adjustingthe amount of power generated by generator 60.

FIG. 2E is a schematic functional diagram illustrating another exampleof engine 18A in FIG. 1 . Engine 18A in the example of FIG. 2E may besubstantially similar to that of the example of FIG. 2B, and likefeatures are similarly numbered. However, in the example of FIG. 2E,engine 18A may be a two and half spool, gas turbofan system compared toa two-spool system such as that shown in FIGS. 2A and 2B. For example,as shown in FIG. 2E, engine 18A includes gearbox 61 and shaft 63 whichcouple fan 28 to LP shaft 58. The rotation of fan 28 is driven by LPturbine 40 via gearbox 61 and shaft 63. In such a configuration, therotational speed of fan 28 may be decoupled from the rotational speed ofLP shaft 58, e.g., with shaft 63 being configured to rotate fan 28 at alower speed than LP shaft 58.

FIG. 4 is a flow diagram illustrating an example technique for operatinga gas turbine engine with a generator coupled to a LP spool assembly inaccordance with examples of the disclosure. For ease of description, theexample technique of FIG. 4 is described with respect to engine system18A shown in FIG. 2B, although any suitable system may implement theexample technique of FIG. 4 , including those other example enginesystems described herein.

As shown in FIG. 4 , during the operation of engine 18A after start-up,e.g., to provide propulsion for aircraft 10 as described above,controller 64 may control generator 60 to generate power at a firstlevel from the rotation of LP shaft 58 (70). The power generated at thefirst level by generator 60 may be used by aircraft to supplyoperational power to one or more of the electrical systems of aircraft10 and/or may be stored in power storage device 66, e.g., for later use.The power generator at the first level may correspond to a first amountof electrical load applied on generator, e.g., for the operation ofelectrical systems 65 and/or power storage device 66. With generator 60operating to generate power at the first level, a first level of torquemay be applied to LP shaft 58 which is in opposition to the rotation ofLP shaft 58.

While generator 60 is operated to generate the power at the first level,engine 18A may provide a first level of thrust for aircraft 10. Thegeneration of power at the first level may be maintained untilcontroller 64 determines that the thrust from engine 18A should bereduced from the first level (72). For example, at some subsequent pointin time, controller 64 may receive a command to reduce the thrustgenerated by engine 18A to decelerate aircraft 10 (72). The reduction inthrust may be associated with an indicating that aircraft 10 shoulddecelerate, e.g., based on an engine thrust lever being reduced by anoperator.

In response to determining that the thrust generated by engine 18Ashould be reduced, the electrical loads from the electrical system 65and/or power storage system 66 may increase (e.g., temporarily) theamount of torque applied to LP shaft 58 in combination with reducing thethrust generated by engine 18A by increasing the level of powergenerated by generator 60 from the first level to a second level greaterthan the first level (74). The increase in amount of power generated bygenerator 60 and, thus, the increase in torque applied by generator 60to LP shaft 58, may be carried out in combination with reducing theamount of thrust generated by engine 18A from a first level of thrust toa second level of thrust that is lower that the first level.

Generator 60 may increase the level of power generated from the firstlevel to the second level using any suitable technique that also resultsin an increase in torque applied to LP shaft 58. For example, controller60 with rectifier/inverter 62 may increase the electrical load appliedon generator 60 by electrical systems 65 and/or power storage 66. Insome examples, to increase the electrical load applied on generator 60,the electrical power supplied to electrical systems 65 for operation maybe taken from generator 60, e.g., instead of other generators or powersources on aircraft 10 and/or the power from generator 60 may directedto power storage, e.g., to charge battery. Rectifier 62 may be used toincrease the power of generator 60 by increasing the electrical loadsapplied by electrical systems 65 and/or power storage 66.

All or a portion of the power generated by generator 60 may be directedto power storage device 66 through rectifier/inverter 62 for storage.Additionally, or alternatively, all or a portion of the power generatedby generator 60 may be used to power one or more of the electricalsystems 65 of aircraft 10. The output voltage of the rectifier 62 on apower bus shared with power storage 66 (e.g., a battery) and/or othergenerators of power of aircraft 10 may be raised to increase the powerfrom generator 60 and, thus, increase the torque applied on LP shaft 58.

In some examples, the increase in power generation by generator 60(e.g., from the increase in electrical load applied on generator 60) maybe selected such that the speed of the LP rotor (e.g., compressor 29 inthe example of FIG. 2B) decelerates consistent with the deceleration ofthe HP rotor speed to ensure the reduction in HP compressor 58 airflowis matched by the corresponding reduction in LP rotor speed to minimizethe excursion of the transient engine operating line towards the LPcompressor stall line. The LP rotor may refer to lower-pressurecompressor 29 and/or fan 28. In the example of FIG. 2D, rather than theLP rotor, the increase in power generation by generator 60 may beselected such that the speed of the IP rotor (IP compressor 31)decelerates consistent with the deceleration of the HP rotor speed toensure the reduction in HP compressor 58 airflow is matched by thecorresponding reduction in IP rotor speed to minimize the excursion ofthe transient engine operating line towards the IP compressor stallline.

In some examples, the increase in power output by generator 60 (with theincrease in load applied to generator 60) may depend on the rate atwhich the thrust from engine 18A is being reduced, e.g., since there maybe a greater deviation from the working line associated with relativelyfast reductions in thrust as compared to the same magnitude thrustreduction but over a longer period of time. The greater the rate atwhich the thrust is reduced, the greater the increase in power generatedby generator 60, e.g., to increase the rate at which the rotationalspeed of LP shaft 58 is reduced by the increased torque application onLP shaft 58. In some examples, the increase in power generated bygenerator 60 may be selected such that the resulting increase in torqueapplied by generator 60 to LP shaft 58 decreases the deviation from aworking line compared to the deviation that may normally result duringthe initial deceleration of aircraft 10 without such an increase intorque applied to LP shaft 58, e.g., as illustrated in FIG. 3B.

In some examples, the increase in torque applied by generator 60 to theLP shaft 58 may increase the rate at which the rotational speed of LPshaft 58 decreases during the reduction in the engine thrust (e.g., therotational speed of LP shaft 58 is decreases at a greater rate comparedto instances in which the torque applied by generator 60 is notincreased). In some examples, the increase in torque applied to LP shaft58 is configured to reduce a time period over which the rotational speedof LP shaft 58 decreases during the reduction in engine thrust (e.g.,the time period that the rotational speed decreases from an initialspeed to a lower speed may be reduced with the application of theincreased torque compared to the amount of time for the speed reductionwithout the application of the increased torque by generator 60). Insome examples, the increase in torque applied to LP shaft 58 isconfigured to decrease the transient deviation of LP compressor 29 fromthe working line of LP compressor 29 during the reduction in enginethrust. In each instance, the increase in torque applied to LP shaft 58may be configured to prevent stall or surge of LP compressor 29 due tothe HP compressor 32 decelerating faster than the LP compressor 29.

While the rotational speeds of HP compressor 32 and LP compressor 29 maybe different in terms of magnitude, both the speed of HP compressor 32and LP compressor 29 may be reduced during a decrease in engine thrust.The increased torque applied by generator 60 to LP shaft 58 may beconfigured to increase the rate at which the LP shaft decelerates, e.g.,to better match the deceleration of HP compressor 32. The increase inpower output of generator 60 (and timing of the power increase) may beselected such that the resulting increase in torque applied to LP shaft58 results in a “matched” deceleration of the LP compressor 29 in viewof the HP compressor deceleration (“matched” with respect to the steadystate compressor operating lines compared to no increase in appliedtorque rather than the HP and LP compressors being matched in absoluterotational speed). Put another way, the increase in power output ofgenerator 60 (and timing of the power increase) may be selected suchthat the resulting increase in torque applied to LP shaft 58 results inless transient deviation from the ‘working line’ for LP compressor 29.In this manner, the increase in torque applied by generator 60 mayprevent LP compressor 29 from going into a stall as a result of notreducing its rotational speed fast enough during the decelerationbecause the HP compressor is decelerating faster reducing the airflow.

In some examples, the power output of generator 60 may be increased byat least about 75 percent or at least about 50 percent, such as, about25 to about 75 percent in combination with the reduction in enginethrust (74). In some examples, the torques applied to LP shaft 58 may beincreased by at least about 75 percent or at least about 50 percent,such as, about 25 to about 75 percent in combination with the reductionin engine thrust (74). However, other values are contemplated.

In some examples, generator 60 may increase power output by at least 200kiloWatts (kW)), such as, about 100 kW to about 300 kW, e.g., byincreasing the load applied on generator 60 by electrical systems 65and/or power storage 66. However, other values are contemplated as theamount of power may be determined by the size and power of an engine andmay be limited by the generator power and size.

One example of this disclosure may be employed by an engine systemincludes a two generators operatively coupled one to the HP rotor/HPshaft 54 and the other to the lower-pressure rotor/shaft 58 (e.g., aswould be the case for engine 18A in FIG. 2B if another generator likegenerator 60 coupled HP shaft 54 such that the rotation of shaft 54 wasused to generate power via the corresponding generator along withgenerator 60). In such a system, the electrical power and hence dragtorque may be increased for generator 60 at the initiation of the enginedeceleration or thrust decrease substantially simultaneously with thereduction in electrical power and drag for a generator (not shown) onthe HP rotor of the same engine. Such a process may have an additionalbenefit as the LP rotor may be slowed and the HP rotor is notdecelerated as rapidly so there is much less mismatch in the LP rotorand HP rotor speeds during the deceleration that would lead tocompressor transient working line migration towards the stall line. Insome examples, this may be accomplished by using LP generator 60 and theHP generator (not shown) to power the same DC power bus and controllingthe proportion of power supplied by each generator using thecorresponding generator rectifier. Raising the voltage of the LPrectifier relative to the HP generator rectifier may increase theproportion of power extracted from the LP generator 60 and henceincrease LP rotor torque offtake at the same time as reducing the HProtor torque offtake.

The thrust from engine 18A may be reduced using any suitable technique.For example, controller 64 may reduce the flow of fuel to the combustorof engine 18A such as combustor 36 of FIG. 2A. The thrust may be reducedby reducing the rate of change at which the fuel is supplied to thecombustor (i.e., reducing the rate of change of the mass flowrate offuel, e.g., as compared to reducing the mass flow rate of the fuelitself). Additionally, or alternatively, the thrust may be reduced byclosing the variable compressor guide vanes or opening of enginecompressor bleed valves.

As noted above, the increase in power generated by generator 60 (e.g.,by increasing the electrical load applied on generator 60 by electricalsystems 65 and/or power storage device 66) may be carried out incombination with the reduction in thrust, e.g., so that the increase intorque applied by generator 60 on LP shaft is in combination with thereduction in thrust. For example, in some instances, the increase inpower generation by generator 60 may be controlled by controller 64 suchthat the power generation increase occurs before or at substantially thesame time at controller 64 initiates the reduction in thrust, e.g., whenthe flow of fuel is reduced. In some examples, the increase in powergeneration by generator 60 may be controlled by controller 64 such thatthe power generation increase occurs less than one second of controller64 initiating the reduction in thrust.

Generator 60 may increase the level of power output by generator 60 fora period of time in combination with the reduction in enginelower-pressure rotor/shaft (e.g., compressor 29/shaft 58) speed andthrust, e.g., before returning to the first level of power that wasgenerated prior to the increase power in response to the reduction inthrust (70). In some examples, the generator power can be reduced oncethe LP rotor/shaft speed is adequately low relative to the HP compressor32 speed which controls the core flow or when the HP and LP speedsclosely match the relationship for steady state engine operation.

FIG. 5 is a flow diagram illustrating another example technique foroperating a gas turbine engine with a generator coupled to a LP spoolassembly in accordance with examples of the disclosure. Again, for easeof description, the example technique of FIG. 5 is described withrespect to engine system 18A shown in FIG. 2B, although any suitablesystem may implement the example technique of FIG. 5 , including thoseother example engine systems described herein. The example of FIG. 5 maybe similar to that of the example of FIG. 4 in that the amount of powergenerated by generator 60 is adjusted to adjust the torque applied to LPshaft 58 during the operation of engine 18A. The adjustment to thetorque in the process of FIG. 5 may be accomplished as described abovefor the process of FIG. 4 . Likewise, the techniques for adjusting thetorque applied on LP shaft 58 with regard to the process of FIG. 5 maybe employed in the process of FIG. 4 . In the example of FIG. 5 , thepower is adjusted in response to the detection of a stall or surge ofengine 18A.

As shown in FIG. 5 , during the operation of engine 18A after start-up,e.g., to provide propulsion for aircraft 10 as described above,controller 64 may control generator 60 to generate power at a firstlevel from the rotation of LP shaft 58 (70). The power generated at thefirst level by generator 60 may be used by aircraft to supplyoperational power to one or more of the electrical systems of aircraft10 and/or may be stored in power storage device 64, e.g., for later use.With generator 60 operating to generate power at the first level, afirst level of torque may be applied to LP shaft 58 which is inopposition to the rotation of LP shaft 58.

While generator 60 is operated to generate the power at the first level,engine 18A may provide a first level of thrust for aircraft 10.Controller 64 may control generator 60 to maintain the generation ofpower at the first level until controller 64 detects a stall or surge ofengine 18A (78). For example, at some subsequent point in time,controller 64 may detect the stall or surge based on a sudden drop incompressor outlet pressure or reversal in air flow direction in thecompressor. A stall condition may be detected when there is a suddendrop in compressor outlet pressure. A surge condition may be detectedwhen there is a sudden large drop in compressor outlet pressure orreversal of compressor air flow direction.

An engine surge or stall could be caused by a bird strike or foreignobject damage in the compressor at high engine power or it could becaused by engine or compressor deterioration. A surge may tend to occurat high engine power conditions whereas a stall may occur at a lowerengine power. It may also be a characteristic of the engine orcompressor whether a stall or surge occurs at a given condition.

In response to detecting a stall or surge of engine 18A, controller 64may increase (e.g., temporarily) the amount of torque applied to LPshaft 58 in combination with the stall or surge of engine 18A byincreasing the level of power generated by generator 60 from the firstlevel to a second level greater than the first level (74). The increasein amount of power generated by generator 60 and, thus, the increase intorque applied by generator 60 to LP shaft 58, may be carried out duringthe stall or surge of engine 18A. The increased amount of torque duringthe stall or surge may cause LP rotor(s) of the LP spool to reduce speedwhile the HP spool remains at a relatively high-speed demanding higherflow. This may cause, e.g., a speed reduction in the lower-pressurecompressor 29 (or fan 28 in the example of FIG. 2C or IP compressor 31in the example of FIG. 2D) working line and allow the compressor 29 torecover from a stall or surge.

Generator 60 may increase the level of power generated from the firstlevel to the second level using any suitable technique that also resultsin an increase in torque applied to LP shaft 58. For example, the loadapplied on generator 60 may be increased from a first level (which maybe zero or non-zero) to a second level by providing additional electricpower input to the battery of power storage 66 and/or electrical systems65 of aircraft 10 such as aircraft electrical accessories. All or aportion of the power generated by generator 60 may be directed to powerstorage device 66 through rectifier/inverter 62 for storage.Additionally, or alternatively, all or a portion of the power generatedby generator 60 may be used to power one or more of the electricalsystems of aircraft 10.

Similar to that described above for an example engine also having agenerator on the HP rotor/shaft (e.g., HP compressor 32/shaft 54), oneexample of this concept is where the electrical power and hence dragtorque is increased for generator 60 at the initiation of the enginedeceleration or thrust decrease simultaneous with the reduction inelectrical power and drag for a generator on the HP rotor of the sameengine. This may provide an additional benefit as the LP rotor is slowedbut the HP rotor is not decelerated as rapidly so there is much lessmismatch in the LP rotor and HP rotor speeds during the decelerationthat would lead to compressor transient working line migration towardsthe stall line.

The increase in power generation by generator 60 may be selected suchthat the LP compressor airflow is better matched with the HP compressorairflow to recovery from the surge or stall and prevent a re-occurrenceof the surge or stall. In some examples, generator 60 may increase poweroutput by at least 200 kW, such as about 100 kW to about 300 kW. In someexamples, the increase in power output by generator 60 may depend on theamount the thrust from engine 18A is being reduced. The more the thrustis reduced, the greater the increase in power generated by generator 60.In some examples, the increase in power generated by generator 60 may beselected such that the resulting increase in torque applied by generator60 to LP shaft 58 decreases the deviation from a working line comparedto the deviation that may normally result during the initialdeceleration of aircraft 10 without such an increase in torque appliedto LP shaft 58, e.g., as illustrated in FIG. 3B.

Generator 60 may increase the level of power output by generator 60 fora period of time in combination with the stall or surge conditiondetected by controller 60, e.g., before returning to the first level ofpower that was generated prior to the increase power in response to thestall or surge detection (70). In some examples, as indicated in FIG. 5, generator 60 may operate to generate the higher level of power outputuntil the stall or surge condition of engine 18A is no longer detectedor present. In some examples, the period of time may be about 4 secondsdepending on the LP speed, e.g., before returning to the first powerlevel or a lower power level.

As described above, some examples of the disclosure employ a generator,such as generator 60, coupled to the shaft of an LP spool assembly toapply an increased level of torque in combination with a reduction inthrust by engine 18A. An example of such a technique is described withregard to FIG. 4 . One condition that may be present with examples ofsuch an approach is that a gas turbine engine may have reduced, andperhaps insufficient stall margin should the generator fail.Accordingly, an engine design and operating procedure may include aFADEC or other controller that reverts to a reversionary logic, whichlimits the acceleration and deceleration rates of the gas turbine enginesuch that stall margin can be maintained. For example, the decelarationrates could be halved in this condition.

Alternatively, or additionally, for emergency scenarios, such as duringan aborted takeoff of an aircraft such as aircraft 10, it may beacceptable to allow the reduced stall margin since a nominal engine mayhave more margin than a deteriorated ‘worst engine’ that must bedesigned for. The impacts of having a stall/surge during and event suchas an aborted takeoff may also be acceptable as the engine cansubsequently be inspected for any damage. FIG. 6 is a flow diagramillustrating an example technique implementing one example of such flowlogic. For ease of description, the example technique of FIG. 6 isdescribed with respect to engine system 18A shown in FIG. 2B, althoughany suitable system may implement the example technique of FIG. 6 ,including those other example engine systems described herein.

As shown in FIG. 6 , controller 64 may determine that an engine thrustlever is reduced (or otherwise receive an input indicating that thethrust of engine 18A should be reduced) (80). Upon receiving the input,controller 64 may determine whether generator 60 is operational (82).For example, controller 64 may determine whether generator 60 isoperational to generate power from the rotation of LP shaft 58 and/oroperational to increase the level of power being generated beyond thelevel currently being generated by generator 60 (82). Controller 64 maymake such a determination by monitoring generator voltage and currentoutputs relative to the expected outputs for this speed in normalnon-failure operation.

If controller 64 determines that generator 60 is operational, controller64 may compute or otherwise determine the rate of thrust level reductionthat is being requested with the received input (84), and then commandrectifier/inverter 62 to increase the power output from generator 60(86). As described above, the specific level of power increase outputtedby generator 60 may be determined based on the amount or rate of thrustlevel being requested (84). Once the power output generated by generator60 is decrease, controller 64 may reduce the flow of fuel to thecombustor of engine 18A to reduce the thrust at the determined rate(88). Controller 64 may then monitor the speed of LP shaft 58 andpressure and/or execute pre-defined commands of power extraction on theLP spool assembly to minimize the deviation from the working line forengine 18A during the deceleration/thrust reduction (90) based on thedeceleration of the HP speed. Once the new thrust level is reached afterthe reduction, controller 64 may then control generator 60 to return toa nominal level of power generation (e.g., the power generation levelprior to the increase in power generation associated with the thrustreduction) (92).

The technique performed by controller 64 upon determining that generator60 is operational (Yes branch of decision 82) may be an example of thetechnique of FIG. 4 , and the technique of FIG. 4 may be carried out bycontroller 64 upon determining generator 60 is operational in theexample technique of FIG. 6 .

Conversely, if controller 64 determines that generator 64 is notoperational (82), then controller 64 may determine if the thrustreduction that is being requested (80) is an emergency thrust reduction(94). Examples of an emergency thrust reduction may include a thrustreduction associated with an aborted (rejected) takeoff, this conditionmay be determined based on the aircraft on ground indication for exampleweight on wheels, and the like. For an aborted (rejected) takeoff theconsequences of an engine surge may be less severe than that for slowengine deceleration where the aircraft may run off the runway.

If controller 64 determines that the requested thrust reduction is anemergency thrust reduction (94), controller 64 may execute a rapid(e.g., typical) deceleration schedule without regard to the stall marginof engine 18A (100). For example, the rate at which the fuel is reducedto the combustor may be reduced at a rate that does not preserve adesired stall margin of engine 18A. The deceleration schedule may bemaintained until the new reduced thrust level is reached (102).Alternatively or additionally, controller 64 may activate bleed valvesor revert to a ‘reversionary bleed valve schedule’ or activate one-timeuse devices such as a burst disk to preserve surge margin.Alternatively, controller 64 may adjust the variable inlet guidevane/variable stator vane (VIGV/VSV) schedule. A stall may be acceptedin some conditions.

If controller 64 determines that the requested thrust reduction is notan emergency thrust reduction (94), controller 64 may execute a reduceddeceleration schedule (e.g., with a slower rate of fuel reductioncompared to the rate employed for the emergency thrust reductioninstance) to preserve a desired stall margin (96). The decelerationschedule may be maintained until the new reduced thrust level is reached(98).

Although examples of the disclosure are described primarily with regardto the low-pressure spool assembly of engine 18A including amotor-generator operably connected to the shaft system of the spool, itis contemplated that such an arrangement may additionally, oralternatively be employed for an intermediate pressure (IP) spool in anengine including three or more spools. For example, in the case of anengine such as engine 18A that includes an HP spool, an IP spool, and alow-pressure spool, the engine may include a motor-generator coupled tothe low-pressure spool shaft, a motor generator coupled to the IP spoolshaft, or both. Regardless of the particular spool, themotor-generator(s) for the IP spool and the low-pressure spool may beoperated in the manner described herein.

Example of the present disclosure may allow for one or more benefitsincluding those described above. In some examples, to achieve anincrease in stall/surge margin, a generator may be “oversized” beyondnormal load requirements. However, to counteract such a designmodification, it is recognized that some generators/electrical machineshave both continuous and transient power ratings. The transient ratingsmay often be double the continuous rating. Since some examples of thedisclosure related to an increase in electrical load to increase torqueapplied by a generator may apply only during transients, examples of thedisclosure may take advantage of the transient power ratings of agenerator to generate significantly more power/torque than wouldotherwise be possible out of generator. Moreover, as aircraft becomemore electrified and/or hybrid electric, there may be an increase in thesize of such electric machines relative to historical sizes and,therefore, they may have an increased effect on the stall/surge margincharacteristics of a gas turbine engine.

As another example benefit, as noted above, engines may incorporatecompressor bleed valves to manage transient periods when there is areduction in thrust and there is a deviation from the working line.However, such bleed valves may be very inefficient. Some examples of thedisclosure may allow for improved engine efficiency by not having to usesuch bleed valves as often. In addition, with reference to FIG. 6 , whenthe LP generator is operational (the Yes path off decision block 82),such an example technique might not use the bleed valves in such manner.Conversely, when the LP generator is not operational (the No path offblock 82), the bleed valves may be activated. Additionally, oralternatively, some examples of the disclosure may allow a reduction inthe size of the bleed valves which can reduce engine size/weight. Also,some examples of the disclosure may enable reduction or elimination ofvariable inlet guide vanes or stator vanes on the IP compressor whichcan reduce engine complexity and save size/weight. In some examples,such bleed valves may be eliminated entirely from an engine.

Various examples have been described. These and other examples arewithin the scope of the following clauses and claims.

Clause 1A. A system comprising a gas turbine engine, the gas turbineengine comprising: a high-pressure (HP) shaft; a HP compressor; a HPturbine, the HP turbine coupled to the HP compressor via the HP shaft; asecond shaft; a second compressor; a second turbine, the second turbinebeing coupled to the second compressor via the second shaft; a generatorcoupled to the second shaft, wherein the generator is configured togenerate electrical power from a rotation of the second shaft, andincrease the electrical power generated by the generator to increase atorque applied to the second shaft by the generator in combination witha reduction in engine thrust.

Clause 2A. The system of clause 1A, wherein the increase in torqueapplied to the second shaft is configured to increase a rate at which arotational speed of the second shaft decreases during the reduction inthe engine thrust.

Clause 3A. The system of clause 1A, wherein the increase in torqueapplied to the second shaft is configured to reduce a time period overwhich a rotational speed of the second shaft decreases during thereduction in engine thrust.

Clause 4A. The system of clause 1A, wherein the increase in torqueapplied to the second shaft is configured to decrease a transientdeviation of the second compressor from a working line of the secondcompressor during the reduction in engine thrust.

Clause 5A. The system of any one of clauses 1A-4A, wherein the increasein torque applied to the second shaft is configured to prevent stall orsurge of the second compressor due to the HP compressor deceleratingfaster than the second compressor.

Clause 6A. The system of clause 1A, further comprising a combustor,wherein the system is configured to reduce the engine thrust by at leastreducing a fuel supplied to the combustor, and wherein the system isconfigured to increase the electrical power generated by the generatorto increase the torque applied to the second shaft such that the torqueon the second shaft is increased at substantially the same time as thereduction in the engine thrust.

Clause 7A. The system of clause 1A, wherein the system is configured toreduce the engine thrust at a first rate when in combination with theincrease in the torque applied by the generator to the second shaft toincrease a rate at which a rotational speed of the second shaft isreduced, and wherein the system is configured to: determine that thegenerator has failed, and reduce the thrust generated by the engine at asecond rate less than the first rate based on the determination that thegenerator has failed.

Clause 8A. The system of clause 7A, wherein the system is configured toreduce the thrust generated by the engine at the second rate by reducinga rate at which the fuel is supplied to the combustor.

Clause 9A. The system of any one of clauses 1A-8A, wherein the secondcompressor comprises a low-pressure compressor.

Clause 10A. The system of any one of clauses 1A-9A, wherein the secondcompressor comprises an intermediate pressure compressor, the gasturbine engine further comprising a fan.

Clause 11A. The system of any one of clause 1A-10A, further comprisingan energy storage device, wherein the increased power generated by thegenerator is stored in the energy storage device.

Clause 12A. The system of clause 11A, wherein the energy storage devicecomprises a battery.

Clause 13A. The system of any one of clauses 1A-12A, wherein theelectrical power generated by the generator is increased in combinationwith the reduction in engine thrust by at least increasing an electricalload applied on the generator, and wherein the increase load applied onthe generator increases the torque applied on the second shaft by thegenerator in combination with the reduction in engine thrust.

Clause 14A. The system of any one of clauses 1A-13A, wherein theelectrical load applied on the generator is increased by at leastchanging a source of electrical power extraction by electrical systemsfrom at least one of an energy storage device or another generator tothe generator.

Clause 15A. The system of any one of clauses 1A-14A, wherein theelectrical load applied on the generator is increased by at least one ofincreasing an electrical load to an energy storage device to thegenerator or increasing the electrical load applied by the electricalsystems to the generator.

Clause 16A. The system of any one of clauses 1A-15A, wherein thegenerator comprises a first generator, the system comprising a secondgenerator coupled to the HP shaft to generate power from a rotation ofthe HP shaft, wherein the first generator increases the torque appliedon the second shaft by at least changing the source of electrical powerto electrical systems and/or an energy storage device from the secondgenerator to the first generator.

Clause 17A. The system of clause 16A, wherein the source of electricalpower to an electrical system and/or the energy storage device ischanged from the second generator to the first generator by at leastincreasing an electrical load applied to the first generator by theelectrical system and/or the energy storage device and decreasing anelectrical load applied to the second generator by the electrical systemor the energy storage device.

Clause 18A. The system of clause 17A, wherein the increased electricalload applied to the first generator by the electrical system and/or theenergy storage device is approximately equal to the decreased applied tothe second generator by the electrical system and/or the energy storagedevice.

Clause 19A. A method for operating a system including a gas turbineengine, the gas turbine engine comprising a high-pressure (HP) shaft; aHP compressor; a HP turbine, the HP turbine coupled to the HP compressorvia the HP shaft; a second shaft; a second compressor; a second turbine,the second turbine being coupled to the second compressor via the secondshaft; and a generator coupled to the second shaft, the methodcomprising: generating, using the generator, electrical power from arotation of the second shaft, and increasing the electrical powergenerated by the generator to increase a torque applied to the secondshaft by the generator in combination with a reduction in engine thrust.

Clause 20A. The method of clause 19A, wherein the increase in torqueapplied to the second shaft is configured to increase a rate at which arotational speed of the second shaft decreases during the reduction inthe engine thrust.

Clause 21A. The method of clause 19A, wherein the increase in torqueapplied to the second shaft is configured to reduce a time period overwhich a rotational speed of the second shaft decreases during thereduction in engine thrust.

Clause 22A. The method of clause 19A, wherein the increase in torqueapplied to the second shaft is configured to decrease a transientdeviation of the second compressor from a working line of the secondcompressor during the reduction in engine thrust.

Clause 23A. The method of any one of clauses 19A-22A, wherein theincrease in torque applied to the second shaft is configured to preventstall or surge of the second compressor due to the HP compressordecelerating faster than the second compressor.

Clause 24A. The method of clause 19A, further comprising reducing theengine thrust by at least reducing a fuel supplied to the combustor, andwherein increasing the electrical power generated by the generator toincrease the torque applied to the second shaft comprises increasing theelectrical power generated such that the torque on the second shaft isincreased at substantially the same time as the reduction in the enginethrust.

Clause 25A. The method of clause 19A, wherein the system is configuredto reduce the engine thrust at a first rate when in combination with theincrease in the torque applied by the generator to the second shaft toincrease a rate at which a rotational speed of the second shaft isreduced, the method further comprising: determining that the generatorhas failed, and reducing the thrust generated by the engine at a secondrate less than the first rate based on the determination that thegenerator has failed.

Clause 26A. The method of clause 25A, further comprising reducing thethrust generated by the engine at the second rate by reducing a rate atwhich the fuel is supplied to the combustor.

Clause 27A. The method of any one of clauses 19A-26A, wherein the secondcompressor comprises a low-pressure compressor.

Clause 28A. The method of any one of clauses 19A-27A, wherein the secondcompressor comprises an intermediate pressure compressor, the gasturbine engine further comprising a fan.

Clause 29A. The method of any one of clause 19A-28A, wherein the systemincludes an energy storage device, wherein the increased power generatedby the generator is stored in the energy storage device.

Clause 30A. The method of clause 29A, wherein the energy storage devicecomprises a battery.

Clause 31A. The method of any one of clauses 19A-30A, wherein increasingthe electrical power generated by the generator to increase a torqueapplied to the second shaft by the generator includes increasing anelectrical load applied on the generator, and wherein the increased loadapplied on the generator increases the torque applied on the secondshaft by the generator in combination with the reduction in enginethrust.

Clause 32A. The method of any one of clauses 19A-31A, wherein increasingthe electrical power generated by the generator to increase a torqueapplied to the second shaft by the generator includes changing a sourceof electrical power extraction by electrical systems from at least oneof an energy storage device or another generator to the generator.

Clause 33A. The method of any one of clauses 19A-32A, increasing theelectrical power generated by the generator to increase a torque appliedto the second shaft by the generator includes at least one of increasingan electrical load to an energy storage device to the generator orincreasing the electrical load applied by the electrical systems to thegenerator.

Clause 34A. The method of any one of clauses 19A-33A, wherein thegenerator comprises a first generator, the system comprising a secondgenerator coupled to the HP shaft to generate power from a rotation ofthe HP shaft, wherein increasing the electrical power generated by thegenerator to increase a torque applied to the second shaft by thegenerator includes increasing the torque applied on the second shaft byat least changing the source of electrical power to electrical systemsand/or an energy storage device from the second generator to the firstgenerator.

Clause 35A. The method of clause 34A, wherein the source of electricalpower to an electrical system and/or the energy storage device ischanged from the second generator to the first generator by at leastincreasing an electrical load applied to the first generator by theelectrical system and/or the energy storage device and decreasing anelectrical load applied to the second generator by the electrical systemor the energy storage device.

Clause 36A. The method of clause 35A, wherein the increased electricalload applied to the first generator by the electrical system and/or theenergy storage device is approximately equal to the decreased applied tothe second generator by the electrical system and/or the energy storagedevice.

Clause 37A. A system comprising a gas turbine engine, the gas turbineengine comprising: a high-pressure (HP) shaft; a HP compressor; a HPturbine, the HP turbine coupled to the HP compressor via the HP shaft; afan; a second shaft; a second turbine, the second turbine being coupledto the fan via the second shaft; a generator coupled to the secondshaft, wherein the generator is configured to generate electrical powerfrom a rotation of the second shaft, and increase the electrical powergenerated by the generator to increase a torque applied to the secondshaft by the generator in combination with a reduction in engine thrust.

Clause 38A. The system of clause 37A, according to any one of clauses2A-18A but with the second compressor being the fan of clause 37A.

Clause 1B. A system comprising a gas turbine engine, the gas turbineengine comprising: a high-pressure (HP) shaft; a HP compressor; a HPturbine, the HP turbine coupled to the HP compressor via the HP shaft; asecond shaft; a second compressor; a second turbine, the second turbinebeing coupled to the second compressor via the second shaft; a generatorcoupled to the second shaft, wherein the generator is configured togenerate electrical power from a rotation of the second shaft, andwherein the generator is configured to, in response to at least one of astall or a surge of the gas turbine engine, increase the electricalpower generated by the generator to increase a torque applied to thesecond shaft by the generator during the at least one of the stall orthe surge of the gas turbine engine.

Clause 2B. The system of clause 1B, wherein the increase in torqueapplied to the second shaft is configured to increase a rate at which arotational speed of the second shaft decreases during the at least oneof the stall or the surge of the gas turbine engine.

Clause 3B. The system of clause 1B, wherein the increase in torqueapplied to the second shaft is configured to reduce a time period overwhich a rotational speed of the second shaft decreases during the atleast one of the stall or the surge of the gas turbine engine.

Clause 4B. The system of clause 1B, wherein the increase in torqueapplied to the second shaft is configured to decrease a transientdeviation of the second compressor from a working line of the secondcompressor during the at least one of the stall or the surge of the gasturbine engine.

Clause 5B. The system of any one of clauses 1B-4B, wherein the increaseis torque is applied to improve recovery from the at least one of thestall or the surge.

Clause 6B. The system of any one of clauses 1B-5B, wherein the secondcompressor comprises a low-pressure compressor.

Clause 7B. The system of any one of clauses 1B-6B, wherein the secondcompressor comprises an intermediate pressure compressor, the gasturbine engine further comprising a fan.

Clause 8B. The system of any one of clause 1B-7B, further comprising anenergy storage device, wherein the increased power generated by thegenerator is stored in the energy storage device.

Clause 9B. The system of clause 8B, wherein the energy storage devicecomprises a battery.

Clause 10B. The system of any one of clauses 1B-9B, wherein theelectrical power generated by the generator is increased in response tothe at least one of the stall or the surge by at least increasing anelectrical load applied on the generator, and wherein the increase loadapplied on the generator increases the torque applied on the secondshaft by the generator in response to the at least one of the stall orthe surge.

Clause 11B. The system of any one of clauses 1B-10B, wherein theelectrical load applied on the generator is increased by at leastchanging a source of electrical power extraction by electrical systemsfrom at least one of an energy storage device or another generator tothe generator.

Clause 12B. The system of any one of clauses 1B-11B, wherein theelectrical load applied on the generator is increased by at least one ofincreasing an electrical load to an energy storage device to thegenerator or increasing the electrical load applied by the electricalsystems to the generator.

Clause 13B. The system of any one of clauses 1B-12, wherein thegenerator comprises a first generator, the system comprising a secondgenerator coupled to the HP shaft to generate power from a rotation ofthe HP shaft, wherein the first generator increases the torque appliedon the second shaft by at least changing the source of electrical powerto electrical systems and/or an energy storage device from the secondgenerator to the first generator.

Clause 14B. The system of clause 13B, wherein the source of electricalpower to an electrical system and/or the energy storage device ischanged from the second generator to the first generator by at leastincreasing an electrical load applied to the first generator by theelectrical system and/or the energy storage device and decreasing anelectrical load applied to the second generator by the electrical systemor the energy storage device.

Clause 15B. The system of clause 14B, wherein the increased electricalload applied to the first generator by the electrical system and/or theenergy storage device is approximately equal to the decreased applied tothe second generator by the electrical system and/or the energy storagedevice.

Clause 16B. A method for operating a system including a gas turbineengine, the gas turbine engine comprising a high-pressure (HP) shaft; aHP compressor; a HP turbine, the HP turbine coupled to the HP compressorvia the HP shaft; a second shaft; a second compressor; a second turbine,the second turbine being coupled to the second compressor via the secondshaft; and a generator coupled to the second shaft, the methodcomprising: generating, using the generator, electrical power from arotation of the second shaft; detecting at least one of a stall or asurge of the gas turbine engine; and increasing, in response to thedetected at least one of the stall or the surge of the gas turbineengine, the electrical power generated by the generator to increase atorque applied to the second shaft by the generator during the at leastone of the stall or the surge of the gas turbine engine.

Clause 17B. The method of clause 16B, wherein the increase in torqueapplied to the second shaft is configured to increase a rate at which arotational speed of the second shaft decreases during the at least oneof the stall or the surge of the gas turbine engine.

Clause 18B. The method of clause 16B, wherein the increase in torqueapplied to the second shaft is configured to reduce a time period overwhich a rotational speed of the second shaft decreases during the atleast one of the stall or the surge of the gas turbine engine.

Clause 19B. The method of clause 16B, wherein the increase in torqueapplied to the second shaft is configured to decrease a transientdeviation of the second compressor from a working line of the secondcompressor during the at least one of the stall or the surge of the gasturbine engine.

Clause 20B. The method of any one of clauses 16B-19B, wherein theincrease is torque is applied to improve recovery from the at least oneof the stall or the surge.

Clause 21B. The method of any one of clauses 16B-20B, wherein the secondcompressor comprises a low-pressure compressor.

Clause 22B. The method of any one of clauses 16B-24B, wherein the secondcompressor comprises an intermediate pressure compressor, the gasturbine engine further comprising a fan.

Clause 23B. The method of any one of clause 16B-22B, the systemcomprising an energy storage device, wherein the increased powergenerated by the generator is stored in the energy storage device.

Clause 24B. The method of clause 23B, wherein the energy storage devicecomprises a battery.

Clause 25B. The method of any one of clauses 16B-24B, wherein increasingthe electrical power generated by the generator to increase a torqueapplied to the second shaft comprises increasing an electrical loadapplied on the generator, and wherein the increase load applied on thegenerator increases the torque applied on the second shaft by thegenerator in response to the at least one of the stall or the surge.

Clause 26B. The method of any one of clauses 16B-25B, wherein increasingthe electrical load applied on the generator increased includes changinga source of electrical power extraction by electrical systems from atleast one of an energy storage device or another generator to thegenerator.

Clause 27B. The method of any one of clauses 16B-26B, wherein increasingthe electrical load applied on the generator increased includes at leastone of increasing an electrical load to an energy storage device to thegenerator or increasing the electrical load applied by the electricalsystems to the generator.

Clause 28B. The method of any one of clauses 16B-27B, wherein thegenerator comprises a first generator, the system comprising a secondgenerator coupled to the HP shaft to generate power from a rotation ofthe HP shaft, wherein the first generator increases the torque appliedon the second shaft by at least changing the source of electrical powerto electrical systems and/or an energy storage device from the secondgenerator to the first generator.

Clause 29B. The method of clause 28B, wherein the source of electricalpower to an electrical system and/or the energy storage device ischanged from the second generator to the first generator by at leastincreasing an electrical load applied to the first generator by theelectrical system and/or the energy storage device and decreasing anelectrical load applied to the second generator by the electrical systemor the energy storage device.

Clause 30B. The method of clause 29B, wherein the increased electricalload applied to the first generator by the electrical system and/or theenergy storage device is approximately equal to the decreased applied tothe second generator by the electrical system and/or the energy storagedevice.

What is claimed is:
 1. A system comprising a gas turbine engine, the gasturbine engine comprising: a high-pressure (HP) shaft; a HP compressor;a HP turbine, the HP turbine coupled to the HP compressor via the HPshaft; a second shaft; a second compressor; a second turbine, the secondturbine being coupled to the second compressor via the second shaft; agenerator coupled to the second shaft, wherein the generator isconfigured to generate electrical power from a rotation of the secondshaft, and increase the electrical power generated by the generator toincrease a torque applied to the second shaft by the generator incombination with a reduction in engine thrust.
 2. The system of claim 1,wherein the increase in torque applied to the second shaft is configuredto increase a rate at which a rotational speed of the second shaftdecreases during the reduction in the engine thrust.
 3. The system ofclaim 1, wherein the increase in torque applied to the second shaft isconfigured to reduce a time period over which a rotational speed of thesecond shaft decreases during the reduction in engine thrust.
 4. Thesystem of claim 1, wherein the increase in torque applied to the secondshaft is configured to decrease a transient deviation of the secondcompressor from a working line of the second compressor during thereduction in engine thrust.
 5. The system of claim 1, wherein theincrease in torque applied to the second shaft is configured to preventstall or surge of the second compressor due to the HP compressordecelerating faster than the second compressor.
 6. The system of claim1, further comprising a combustor, wherein the system is configured toreduce the engine thrust by at least reducing a fuel supplied to thecombustor, and wherein the system is configured to increase theelectrical power generated by the generator to increase the torqueapplied to the second shaft such that the torque on the second shaft isincreased at substantially the same time as the reduction in the enginethrust.
 7. The system of claim 1, wherein the system is configured toreduce the engine thrust at a first rate when in combination with theincrease in the torque applied by the generator to the second shaft toincrease a rate at which a rotational speed of the second shaft isreduced, and wherein the system is configured to: determine that thegenerator has failed, and reduce the thrust generated by the engine at asecond rate less than the first rate based on the determination that thegenerator has failed.
 8. The system of claim 7, wherein the system isconfigured to reduce the thrust generated by the engine at the secondrate by reducing a rate of change at which the fuel is supplied to thecombustor.
 9. The system of claim 1, wherein the second compressorcomprises a low-pressure compressor.
 10. The system of claim 1, whereinthe second compressor comprises an intermediate pressure compressor, thegas turbine engine further comprising a fan.
 11. The system of claim 1,further comprising an energy storage device, wherein the increased powergenerated by the generator is stored in the energy storage device. 12.The system of claim 11, wherein the energy storage device comprises abattery.
 13. The system of claim 1, wherein the electrical powergenerated by the generator is increased in combination with thereduction in engine thrust by at least increasing an electrical loadapplied on the generator, and wherein the increase load applied on thegenerator increases the torque applied on the second shaft by thegenerator in combination with the reduction in engine thrust.
 14. Thesystem of claim 1, wherein the electrical load applied on the generatoris increased by at least changing a source of electrical powerextraction by electrical systems from at least one of an energy storagedevice or another generator to the generator.
 15. The system of claim 1,wherein the electrical load applied on the generator is increased by atleast one of increasing an electrical load to an energy storage deviceto the generator or increasing the electrical load applied by theelectrical systems to the generator.
 16. The system of claim 1, whereinthe generator comprises a first generator, the system comprising asecond generator coupled to the HP shaft to generate power from arotation of the HP shaft, wherein the first generator increases thetorque applied on the second shaft by at least changing the source ofelectrical power to electrical systems and/or an energy storage devicefrom the second generator to the first generator.
 17. The system ofclaim 16, wherein the source of electrical power to an electrical systemand/or the energy storage device is changed from the second generator tothe first generator by at least increasing an electrical load applied tothe first generator by the electrical system and/or the energy storagedevice and decreasing an electrical load applied to the second generatorby the electrical system or the energy storage device.
 18. The system ofclaim 17, wherein the increased electrical load applied to the firstgenerator by the electrical system and/or the energy storage device isapproximately equal to the decreased applied to the second generator bythe electrical system and/or the energy storage device.
 19. A method foroperating a system including a gas turbine engine, the gas turbineengine comprising a high-pressure (HP) shaft; a HP compressor; a HPturbine, the HP turbine coupled to the HP compressor via the HP shaft; asecond shaft; a second compressor; a second turbine, the second turbinebeing coupled to the second compressor via the second shaft; and agenerator coupled to the second shaft, the method comprising:generating, using the generator, electrical power from a rotation of thesecond shaft, and increasing the electrical power generated by thegenerator to increase a torque applied to the second shaft by thegenerator in combination with a reduction in engine thrust.
 20. Themethod of claim 19, wherein the increase in torque applied to the secondshaft is configured to increase a rate at which a rotational speed ofthe second shaft decreases during the reduction in the engine thrust.